Gels can exhibit phase transition, or significantly large volume change, in response to variation of the surrounding conditions. For example, the fluids supporting a gel can be modified to cause a significantly large contraction or expansion of a gel such as by changing the pH, solvent composition, relative concentration of solvents, solvent temperature, or the ion concentration of the fluid.
However, phase transition of gels generally has been dependent upon generating an interaction between a gel polymer network, comprising a single polymer and a phase-transition-modifying agent, or upon intramolecular interactions between like-strands of the polymer network. Also, phase transition caused by changes in fluid temperature have heretofore been limited to significantly large contraction during an increase in temperature and, conversely, a significantly large expansion during a decrease in temperature.